一种新的无位置传感器BLDC控制方法

Fig.1.LocationofeightpossiblestationaryvoltagevectorsforaVSIinthed-qplaneaccordingtotheswitchingfunction(Sa,Sb,Sc)ANewStartingMethodofBLDCMotorswithoutPositionSensorWook-JinLeeandSeung-KiSulSchoolofElectricalEngineeringandComputerScienceSeoulNationalUniversitySeoul,[e-mail]@plaza.snu.ac.krAbstract—ThispaperpresentsanovelmethodtodetecttherotorpositionoftheBrushLessDC(BLDC)motorofaHardDiskDrive(HDD)atstandstillandastart-upmethodtoacceleratetherotoruptoacertainspeedwheretheconventionalpositionsensorlesscontrolmethodsbasedonthebackEMFcouldworkreasonably.TheproposedinitialrotorpositionestimationmethodissuitabletoavoidthetemporaryreverserotationorthestartingfailureofHDD.TheprincipleoftheestimationisbasedonthevariationofthecurrentresponsecausedbythemagneticsaturationofthestatorcoreofBLDCmotorwhenthecurrentflowsalongthemagneticaxis.ThismethodcanbeimplementedusingonlyonecurrentsensoratDClinkoftheinverter,thatisprerequisiteforHDDdrive.Itdoesnotdependonthemodelofthemotor,anditisrobusttomotorparametervariations.Bytheproposedmethod,itisdemonstratedexperimentallythatastablestartingcanbeachievedevenwithseveremechanicaldisturbance.Keywords-BLDCmotor;HDD;sensorless;starting;saturationI.INTRODUCTIONRecentlysensorlessoperationofbrushlessdc(BLDC)motorusingtheback-EMFinformation,suchasback-EMFzerocrossing,iswidelyusedandadequateforsmallorlow-costapplicationsuchasHardDiskDrive(HDD).Butwhenthemotorisatstandstilloratlowspeed,itisimpossibleorverydifficulttogetthepositioninformationfromback-EMF.Therefore,aspecialstartingmethodisgenerallyneeded[1].InHDDthepowersupplyvoltageisgettingreduced,andthedetectionofrotorpositionfromback-EMFisgettingdifficultatthelowspeed.Furthermore,recentlyHDDiswidelyspreadintothemobileapplicationssuchasportablePCandPDA.So,thestablestartingandaccelerationtonominaloperatingspeedregardlessofseveremechanicalshockisutmostconcernintheseapplications.Initialrotorpositionestimationisimportantnotonlyforthestablestartingbutalsoforthemaximumstartingtorquetoreducestart-uptimeofHDD.Onepopularmethodtoestimatetheinitialrotorpositionatstandstillisutilizationofthesaturationeffectofstatorironcoreduetothepermanentmagnet[1-5].Astatorinductancevarieswiththerotorpositionduetothesaturationcausedbyrotormagnet,sodoestherateofchangeofthecurrentinthestatorwindingwhenaconstantvoltageisappliedtothewindings.Bythemeasurementoftherateofthechangeofcurrentinthestatorwindingduetothechangeofinductance,itispossibletoestimatetherelativepositionbetweenarotormagnetandastatorwinding.TheinductanceofthestatorwindinghasitsminimumvaluewheretheNorthpoleoftherotormagnetliesinthecorrespondingstatorwindingaxisinthecaseofthespindlemotoroftheHDD.Severaldirectionsofvoltagevectorscanbeappliedtothestatorwindingofthemotortoidentifytherotorposition,andthedirectionthathasminimuminductancecanbedecidedasthed-axisdirection[2].UsingasinglecurrentsensorinDClinkoftheinverter,withconventionalmethod60degreesofresolutionintheestimationofrotorpositionispossibleatbest,becausetheavailablevoltagevectorswithPWMinverterarerestrictedtothebasicsixnonzerovoltagevectors.InFig.1,theavailablevoltagevectorswitha3-phasevoltagesourceinverterarerepresented.Asthestartingmethodfromstandstilltoacertainlowspeed,variousmethodswhichinjectextravoltagepulsesperiodicallytomeasurethestatorinductancevaryingwiththerotorpositionwereproposed.[4,5]However,thesemaynotbeacceptableinHDDbecauseoftheircomplexity.Asasimpleandconventionalmethodtorotatethemotoratstandstill,apre-determinedvoltagewaveformhadbeenapplied.Thentherotormightrotatesynchronouslywiththeappliedvoltage[1,6].Inthismethod,theelectricalandmechanicalparameterssuchasthetorqueconstant,thefrictioncoefficient,andtheinertiaoftherotorshouldbeconsideredforthestablestartingperformance.Someunexpecteddisturbanceorloadtorqueduringstartingproceduremaycauseseriousstartfailures[1].2397IAS20040-7803-8486-5/04/$20.00©2004IEEE(a)EquivalentcircuitofthemotorwhentheV1voltagevectorapplied(b)DC-linkcurrentwaveformwhenavoltagevectorappliedFig.2.Theinductancemeasurementmethodofthestatorwindingbyapplyingonevoltagevectorduringasamplingtime(Ts)(a)MeasuredDC-linkcurrentsamples(b)MeasuredstatorwindinginductanceFig.3.StatorinductanceasafunctionofrotorpositionII.PROPOSEDINITIALROTORPOSITIONESTIMATIONMETHODA.InductancevariationduetothemagneticsaturationTheestimationoftherotorpositionisbasedonthenonlinearmagnetizationcharacteristicsofthestatorcore.Thestatorcoreclosetoamagneticpoleofpermanentmagnetoftherotorisstronglymagnetized.Therefore,ifastatorwindingisclosetothemagneticpoleoftherotor,theratioofthechangeofthecurrentinthestatorwindingflowinginthemagnetizingdirectionislargecomparedwiththatintheoppositedirectionbecauseofthemagneticsaturationofthestatorcore.SothevalueofthecurrentwouldbedifferentaccordingtotherotorpositionifaconstantvoltagevectorfromPWMinverterisappliedtothestatorwindingofthemotorforaconstanttimeperiod.Fig.2showsthedetailedinductancemeasurementmethodthatisincaseofV1voltagevectorapplied.Themotorismodeledasa3-phaseR-LcircuitasshowninFig.2